Fluid pressure sensitive gauge



Dec. 9, 1952 E. x. SCHMIDT 2,620,666

FLUID PRESSURE SENSITIVE GAUGE Original Filed Dec. 6, 1947 2 SHEETS-Sl-IEET 1 Dec. 9, 1952 x. SCHMIDT 2,620,666

FLUID PRESSURE SENSITIVE GAUGE Original Filed Dec. 6, 1947 2 SHEETS-SHEET 2 Patented Dec. 9, 1952 UNITED STATES PATENT OFFICE FLUID PRESSURE SENSITIVE GAUGE Edwin X. Schmidt, Chenequa, Wis., assignor to Cutler-Hammer, Inc., Milwaukee, Wis., a corporation of Delaware Original application December 6, 1947, Serial No.

790,210. Divided and this application January 17, 1948, Serial No. 2,830

erally offset portion l3 carrying a bolt 15 which 2 is threadedly adjustable with respect theretothe shanks of the two bolts l5, 15 being adapted for cooperation with lugs or projections I, Ill carried by tank ID to control the height or posiapplication, Serial No. 790,210, filed December tion of the respective meters within said tank. 6, 1947, for Methods of and Apparatus for Con- By proper adjustment of one or the other or both tinuously Analyzing Gases. of the bolts l5, IS the normal capacities of the An object of the invention is to provide a novel meters l l and I2 may be equalized at a predeterform of gauge which is particularly adapted for mined value for any given height of the body of use with gas analyzing apparatus of the charac- 10 liquid l6, preferably mercury, within tank I0. ter disclosed in my aforementioned abandoned The method of effecting adjustment of the meters application, Serial No. 790,210 (although not limto provide normally equal capacities thereof is a ited to such use), whereby the accuracy of the known expedient, and inasmuch as such method indication and/or recording of a value or values forms no part of the present invention a detailed ascertained by a metering apparatus is substanl5 description thereof is deemed unnecessary. tially increased, and the time lag of the instru- Meters H and I2 are adapted to be simultanement as a whole is reduced to a minimum. ously rotated at like rates, as y eans of a p i Another object is to provide an improved form of like gears H, I! which are keyed or otherwise of gauge of the constant volume type adapted for d y secured t S ft -Sa d g ars respecgenera1use 9,1 tively meshing with gears or gear teeth ll, 12*, Other objects and advantages of the invention Which are preferably formed i a ly wi one i hereinafter appeen side wall portion of each of said meters. Shaft The accompanying drawings illustrate certain 14 is d v at y Suitable Speed y a mOtOr embodiments of the invention, which will now be which i hown ppor ed upon a bracket 19 atdescribed; it being understood that the emboditeched to an Outer S de Wall of the tank Ill. The ments illustrated are susceptible of modification aforementioned normally fixed bearings f r e in respect of certain structural details thereof respective meters are designated by the numerals without departing from the scope of the appended i l c and l claims The flue gas, or other gas to be tested, is sup- In t drawings plied (as by a pump, not shown) through conduit Figure 1 illustrates schematically a gas analyz- 20 t a y Suitable pressure, W c is p ly ing apparatus having one form of my improved greater than atmospheric pressure. Located pressure gauge associated therewith to continu- Within Conduit 29 is restriction, Shown diaously indicate the volumetric proportionality of a giemmaticelly at 2| At the delivery nd of barconstituent removed from a gas under test, and i 2| there is p d an Open ended branch Fig. 2 similarly schematically illustrates a gas p p 22 Which y Communicate direct y with anejyzing apparatus adapted t continuously atmosphere. The barrier 2| restricts the flow of move a multiplicity of difierent constituents of a s to Such a Value t at Sa d gas is able to escape test gas, during passage of the latter in sequence through p 22 Without raising the pressure 1113011 between adjacent positive displacement liquid the dellvery Side of barrier 2i above atmospheric type meters or pumps of a multiple series; the Pressure, and the Outward flow of gas t ro g structure of the gauges shown in this figure being pipe 22 ti e y prevents induction o ry slightly different from that shown in Fig. 1. 1his means the gas is supp ied through pipe 23 Referring first to Fig. 1, the numeral [0 d to the inlet end of meter I! at atmospheric presignates a suitable tank or container within which Surea pair of meters or pumps and are adapted may be assumed. the meters and to be supported. Meters H and I2 are preferably are each initially ju ted, with respect to of the character disclosed in my Patent No. the level 0f the body f mercury l6 within 1,447,437, dated March 6, 1923. Said meters are container as to provide r e iv ry by each rotatably supported within bearings arranged in of tWO cubic inches of test or ther gasnormally fixed relation to tank It, as by means 50 ous fluid, per minute. If the outlet of meter ll of a pair of lik yoke members [3, [3, which are were directly connected with the inlet of meter in turn supported by a driving shaft 14 which is 12 it is ObVieuSthat the me quantity of test gas rotatable with respect thereto. Each yoke I3 is Would he passed gh and delivered by both preferably provided at its upper end with a latmeters p unit of time. and hence there would be a common level H5 of the mercury within tank I and within the inlet and outlet ends of each of the meters I I and I2it being noted that said meters are respectively provided with openings H H and IF, I2 whereby the body of mercury I5 is free to move from each meter to the other, and from the inlet to the outlet, and vice versa, of each meter.

As disclosed in Fig. 1, however, the test gas is adapted to pass from meter II by conduit 24 through an absorbing medium, represented diagrammatically by the numeral 25, and thence by conduits 26 and 2'! to the inlet end of meter I2. If it be assumed that the test gas is flue gas, and if it is desired to ascertain the proportional quantity or value of carbon dioxide contained therein, the absorbing medium therefor may consist of a dry material, such as soda lime. If it is desired to employ a medium of the liquid type for absorbing the carbon dioxide, or for absorbing carbon monoxide, or oxygen, or another constituent of the flue gas, I prefer to employ any well known means (not shown) for drying the gas sample prior to its passage through the aforementioned orifice 2 I.

If the volume of gas passing through meter I2 is less than that passing through meter II (due to reduction in volume of the gas sample by the action of the absorbing medium 25 in removing a constituent thereof), meter I2 will pull a vacuum 0n the absorption chamber 25, which will correspondingly raise the level of mercury I6 at the inlet end I2 of meter I2thereby reducing, by a proportional amount, the capacity of meter I2. The level of mercury IE5 at the inlet end I2 of meter I2 will continue to rise until the capacity of meter I2 equals the volumetric rate of delivery of gas thereto. By measuring the difference between the level of mercury It at the inlet end I I of meter II and the level of mercury I8 at the inlet end I2 of meter I2, I am able to ascertain the difference in volumetric rates of delivery of meters II and I2.

In practice the initial surface areas of the mercury IS in the inlets II and I2 and outlets II and I2 of the meters II and I2 are all equal to each other, and each of said surface areas is preferably only a small fraction of the total surface area of the entire body of mercury It. Thus, each of said inlet and outlet surface areas may be equal to one per cent. (or one one-hundredth) of the total surface area of the body of mercury I6. Accordingly, the aforementioned difference in the liquid levels in inlets II and I2 of said meters can conveniently be indicated! and/or recorded by means of a gauge which measures the difference in pressure between the inlets II and I2? This gauge may be calibrated to indicate directly the percentage value of the volume of gas absorbed in the absorption chamber 25.

With further reference to Fig. 1, it is to be understood that the gas sample is discharged from the outlet end I2 of meter I2 through conduits I2 I2 and I2 to atmosphere-either directly as indicated, or through the medium of a flue or smokestack (not shown) wherein substantially atmospheric pressure obtains.

The operation of the device shown in Fig. 1 is as follows: Assume that the instrument is initially operating without absorption (as, for instance, when air is being passed through both meters I I and I2), and indicating zero per cent. absorption. If then the sample of flue gas from which the constituent (say, carbon dioxide) is to be absorbed is passed through conduit 23 to and through meter II, and thence through absorber 4 25 and meter I2; and if the volumetric proportionality of said constituent is 10 per cent. of the total volume of the flue gas samplethe instantaneous rate of delivery to meter I2 would fall to per cent. of the volumetric rate of flow through meter II. With this decreased net delivery rate to the inlet chamber IZ of meter I2, the pressure in said inlet chamber I2 would decrease and the level of the mercury body It therein and in the outletchamber II of meter I I would rise, whereas the level of the mercury body IS in the inlet chamber I I of meter I I would fall. The capacity of meter I2 would thereby be reduced-that of meter II would be increased slightly (because of the decrease in the mercury level in the inlet I I of meter II) ;-the pressure difference between the inlet II of meter II and the inlet I2 of meter I2 increasing. As this pressure difference, which may be taken as an indication of gas concentration (that is, as an indication of the percentage content of said constituent in the gas sample), approaches the value satisfying the equation forstable pressure, an indication is obtained which is directly related to the partial pressure of the gas constituent removed from the gas sample by the absorbing medium 25.

Thus with the meter II delivering 'two cubic inches of flue gas per minute, and with the combined displacement of gas by the rise in liquid level in the inlet of meter I2 and in the outlet of meter II of .006 cubic inch for each per cent of change in the indication of the value of the constituent to be removed; starting with 'a 10 per cent difierence between indication and absorption, during the reduction of indication from 10 per cent to 5 per cent, average difference 7 per cent, (.006) (5)+(.()'75) (2) minutes, or 12 seconds would be required. Similarly, in again halving the diiference between indication and absorption, an additional 12 seconds would be required, etc.

If it be assumed that it is desired to indicate the percentage value of the removed constituent within plus or minus one-fourth of one per cent (for example, COzl2 per cent, within 11% per cent and 12 per cent), and the concentration should change substantially instantaneously from 12 per cent to 11 per cent, this would require 24 seconds before the indication reaches 11 /4 per cent. Similarly, for ascertaining smaller concentrations, for the same 8.3 per cent change in the amount of absorption, 24 seconds would be required before the indication reaches the new value within 2 per cent of the actual concentration. With a change in concentration of double this amount the time vrequired to indicate within 2 per cent of the actual concentration would be increased by 12 seconds.

With power driven liquid displacement meters II and I2 of equal capacities connected in series, with the absorption chamber 25 following meter II, as shown; with the pressure at the inlet end II of meter II equal to the pressure at the outlet end I? of meter I2; and with no (or zero) absorption by absorber 25, the pressures in the inlet and outlet ends of meters II and I2 will all be equal to each other.

A change in the distribution of the mercury sealing liquid in the various parts of the meters II and I2 changes the volumetric displacement of said meters. The relative levels of the body of mercury I6 in the various parts of the meters II and I2 depend upon the relative pressures of the test gas at different points in its flow through said meters; and if the flow of the mercury body It from one point to another offers no pressure drops, said relative levels are directly related to the differences in said pressures. The delivery rates of meters II and I2 depend not only upon their volumetric displacements (which depend upon the mercury level at the inlet end of ach), but also upon the respective inlet pressures in said meters.

It may be pointed out that any increase in fluid pressure in the outlet end l l of meter H as compared with the fluid pressure at the inlet end l2 of meter l2 (such as would result from a pressure drop through the absorber 25) would increase the level of mercury in each of the remaining three chambers (I I I2 and H by an equal amount. If the surface area of mercury in the outlet end H of meter II is one per cent. of the total surface area the fall in level of mercury in the outlet end I l of meter H would be ninety-nine per cent. of the total pressure drop through absorber 25 and the rise in level in the remaining three ends H l2 and l2 of the meters would be one per cent. of the total pressure drop. Since the mercury level in meters II and [2 would rise to like amounts (at the respective ends H and l2 thereof) due to this pressure drop, the volumetric capacities of the meters would be decreased by substantially like amounts and the relative capacities of the two meters would be substantially unaffected by the pressure drop through the absorber 25.

Similarly, a difference in pressure between the inlet H of meter II and the outlet I2 of meter l2 would only slightly affect the level in the inlets II and [2 of the respective meters and in the outlet I l of meter I I, and would only slightly affect the relative volumetric capacities of the two meters.

In Fig. 1, the conduit 29 communicates with a closed chamber 30. Chamber 3!! contains a predetermined quantity 3! of mercury, upon which an inverted cup-shaped float member or prover bell 32 is adapted to rest. A conduit 33 extends from the outlet end of absorber 25 into chamber 30 and upwardly through the body of mercury 3| and opens to the interior of bell 32 at a point above any level to be attained by mercury 3| therewithin during operation of the device. Rigidly attached to the closed upper end of bell 32 is a rod or stud 34. A lever 35 has one end thereof pivotally connected with stud 34 intermediate the ends of the 1atter-said lever having an upwardly angled portion lie a substantially horizontal portion 35 a downwardly extending substantially U-shaped portion 35 (which is pivotally supported by a pin 35) a second substantially horizontal portion 35 and a portion 35 with which an adjustable counterweight 35 has threaded engagement. Extending outwardly from portion 35 and insulated therefrom as indicated at 35 is a contactor 35 Contactor 35* is movable upwardly into engagement with a stationary contact 31 upon a predetermined degree of downward movement of bell 32, or downwardly into engagement with a stationary contact 38 upon a predetermined degree of upward movement of said bell.

As shown, the pivot pin 36 is located within a pocket 39 formed on the outer surface of the wall 30 of chamber 30; said pocket containing a quantity of liquid 40, such as mercury or water; and a vane or partition 39 extending outwardly from wall 30 and then downwardly into pocket 39, below the level of liquid 40, whereby lever 35 is free to pivot upon pin 36, whereas the interior 6 of chamber 30 is sealed from the exterior thereof. Inasmuch as the interior of chamber 30 is subjected to atmospheric pressure by the means aforedescribed, the sealing liquid 40 might, of course, be omitted. Such seal, however, positively insures subjection of the exterior of bell 32 to the pressure of test gas as supplied to the first meter ll of the series. The contactor 35 cooperates with contacts 31 and 38 to control the operation or inoperation of a split-field reversible motor 4lthe latter, when operated, acting through gearing 42 and 43 to effect rotation of a shaft 44 in one direction or the other. Shaft 44 has attached thereto a spool 45 to which the opposite ends of a flexible cord or wire 46 are connected. Cord 45 passes around a pair of spaced pulleys or rollers 41 and 48, and has attached thereto at a predetermined point an indicating element 49 for cooperation with a suitable scale 50. Scale 5?] is preferably calibrated as shown to afford indication of the percentage or proportional volume of a constituent of the test gas.

Shaft 44 is mounted for rotary movement within a hollow upward extension 30' of chamber 30; said shaft being restrained against substantial upward or downward displacement relatively to said extension. Shaft 44 is provided with a threaded lower end portion 44 which cooperates with a threaded opening in the upper end 51 of a tubular metal member 5| which is slidable within the recess 3! in extension Sc -one side wall of said recess having a groove 33 and end 5P having a lateral projection 51 cooperating therewith to prevent rotation of said member 5|. The lower end of member 51 is flared at 5 I and rigidly connected with a ring portion 51 which is adapted to be immersed to a variable degree within the body of mercury 3| in chamber 3s). A spring 52 is interposed under a predetermined degree of initial tension between the upper end of stud 34 and a point 55 in the length of member 5i. A packing nut or gland may be arranged to surround shaft 44, as shown more or less diagrammatically at 53. The flared portion 5| c is cut away, as shown at El to equalize the pressures within and outside of member 5! and to permit lever 35 to act therethrough.

Inasmuch as the upper surface of bell 32 is subjected to atmospheric pressure (by communication of chamber 30 with conduit 29), it is to be understood that initial balancing of the parts will be effected by subjecting the interior of bell 32 to atmospheric pressure. Such balancing may be effected by passing through pump i I, absorption chamber 25 and pump l2, air or a similar gas which is unaffected by the absorbing medium; or by passing the test gas through pumps l l and [2 in series, while shunting the chamber 25 by any suitable means (not shown).

During such initial adjustment of the device of Fig. 1 (when no constituent is being removed from the gas or air during its passage seriatim through meters II and I2), the contactor 35 will be automatically moved into engagement with contact 38 to effect operation of motor 4! in a direction to return indicator 49 toward the zero position on scale as; whereupon ccntactor 35 assumes the intermediate or balanced posi tion thereof illustrated-or the same may be balanced by manual adjustment of the position of weight 35 If necessary, the pointer or indicator 49 may be loosened and moved along cable 46 to the zero position of the scale 53, and then again clamped to said cable.

As will be apparent, the gauge illustrated in Fig. 1 is of the constant volume type. The degree of tension upon spring 52 depends only upon the weight of the bell or float 32, plus the weight of that portion 3! of the mercury 3| inside of the bell which is above the level of said mercury outside of said bell. It is also very slightly affected by the weight of mercury 3| displaced by the side walls of bell 32. If the last mentioned eiiect is neglected, and ii bell 32 is maintained in substantially the same position at all times, the top support (point P of member 5|) will then assume a position which is directly related to the difference in pressure between the inside and outside of bell 32-regardless of the actual levels of the mercury inside and outside of said bell the displacing ring portion 5| cooperating with the body of mercury 3| to provide for attainment of this result.

Let it be assumed that a decrease in the inlet pressure of meter |2 occurs. Such decrease in inlet pressure, by virtue of conduit 33, results in arise in the level of mercury 3 in bell 32 and in a consequent decrease in the level of the mercury in chamber 39 outside of bell 32. If the displacer ring 5 i were omitted, the result would be that the volume of the gas in bell 32 above the level of mercury Lil would decrease.

However, in the present gauge as the level of mercury 3| rises in the bell 32, an increase in the force exerted by bell 32 and the weight of mercury therein above the level of mercury outside the bell on lever 35 occurs, and the latter is caused to move in the counterclockwise direction, as viewed in Fig. l, to engage its portion 35* with contact 37. Motor Al would consequently be energized to drive shaft M in a direction such that displacer member 5| would be raised relative to the bottom end of chamber 3!). Such raising of displacer member 5| results in progressive decrease in the amount of mercury displaced by displacer ring 5| and accordingly the level of mercury in chamber decreases. Such decrease in the level of mercury in chamber 30 occurs both inside and outside of bell 32, and consequently the counterclockwise force exerted by bell 32, and the weight of mercury therein above the level outside thereof, on lever decreases. Ultimately such counterclockwise force rebalances with that exerted by spring 52 and lever 35 again reaches its balanced position shown in Fig. 1 wherein its portion 35 disengages from contact 3?. When such condition of rebalance of lever 35 occurs, if displacer ring is of proper size, the volume of gas (and the consequent pressure thereof) will be the same as that preceding the assumed decrease in pressure at the inlet of meter l2. It will be appreciated that the gauge will function in the reverse manner from that hereinbefore described upon a decrease in inlet pressure at meter l2.

If desired, displacer ring 5| could be selected of such size that the volume of gas inside bell 32 actually increases with a decrease in pressure of test gas and vice versa. With such a negative change of capacity inside of bell 32, the positive change in capacity of the inlet head |2 of meter i2 and outlet head for the same change in pressure may theoretically be neutralized. However, from the viewpoint of practicality it is desirable to slightly under-compensate for the sake of stability and by the use of a device like that shown in Fig. l I am enabled to appreciably reduce the time lag in responding to changes in the proportionality of the absorbed constituent of the test gas, the tendency of the device to hunt bemg considerably reduced by the under-compensation.

Although I have shown the element 49 as an indicator for cooperation with scale 5il--it will be apparent to those skilled in the art that the same may have attached thereto a recording stylus or pen for cooperation with a power driven record chart (not shown) of any suitable form;

In Fig. 2 I have illustrated schematically a gas analyzing apparatus for ascertaining the instantaneous proportional or percentage value of three different constituents (such as carbon dioxide, carbon monoxide, and oxygen) of the test gas. Such apparatus involves use of a series of four meters |2, 54 and 55, of like form and size, and a series of three gauges 64, of like form and sizethe gauges shown in Fig. 2 being of more simple construction than that of Fig. 1, and the same being rigged to provide for automatic and simultaneous indication and recordation of the several values to be ascertained. Thus the tank It may be similar to but correspondingly larger than that shown in Fig. l and the meters H, I2, 5d and may be connected with a common driving motor (not shown), such as the motor I8 aforedescribed.

The test gas may be supplied by a pump P for flow through a conduit 20 and orifice or restriction 2|, to conduit 23---whose upper end 22 is open to the atmosphere-whereby the test sample as supplied to the inlet end of meter H is at substantially atmospheric pressure. The outlet end of meter i is connected by conduit 25 with the absorbing chamber 25, wherein a constituent of the gas (say, carbon dioxide) is removed. The outlet end of absorbing chamber 25 is connected by one branch conduit 2'1 with the inlet end of meter l2, and by another branch conduit 33 with the inside of bell 32 above the highest point which the level 3H of the body of mercury 3| will attain within said bell. The body of mercury 3| is contained within a tank 58 which is open to the atmosphere, wherefore the exterior of bell 32 and the body of mercury 3| outside of said bell are subjected to atmospheric pressure.

The stud 34 extending upwardly from bell 32 is pivotally connected at 59 to a contactor lever 69, whose left-hand end is pivotally attached at El to a bracket 62 which is rigidly connected to tank 58. The contactor 66 is connected to the righthand end of lever 68, and is insulated therefrom, as indicated at Eb said contactor being adapted to cooperate with upper and lower stationary contacts 31 and 38, to efiect operation of motor 4| in one direction or the other, as described in connection with Fig. 1. Motor 4! is connected through gears 42 and 43* with a shaft 63, whose threaded lower end 83* cooperates with the correspondingly threaded portion 64 of an upward extension 64 of ring 54 to efiect upward or downward displacement of the latter, with a consequent variation of the level of the body 3| of mercury exteriorly of bell 32, to effect return of bell 32 and the contactor to the intermediate or neutral positions thereof illustrated. A coiled spring 52 is interposed under a predetermined degree of tension between the upper end of stud 34 and the aforementioned portion 64 so that the tension of said spring is varied with the raising or lowering of displacement ring 64. Shaft 63 has non-rotatably attached to its upper end a grooved wheel or the like 65 to receive the left-hand end portion of an endless cord or cable 66, whose right-hand end portion is tted into a groove of a spool 61 which is rotatably supported by a pin 68.

Cord 66 has attached thereto at a predetermined point an indicating and recording stylus 89, which is adapted to cooperate with the lefthand section w of a chart H! which is adapted for continuous movement at a constant rate by any suitable or well known means, such as a clockwork (not shown). The chart section 10 is preferably calibrated to afford instantaneous indication and simultaneous and continuous recordation of the proportional or percentage value of the carbon dioxide in the test gas.

After passage through the second meter E2 of the series, the flow of test gas (reduced in volume to a degree corresponding to the proportional value of the first mentioned constituent, carbon dioxide, which has been removed therefrom) passes through the second absorbing chamber 25 which is adapted to remove another constituent, such as carbon monoxide. The outlet end of chamber 25 communicates through a branch 27 with the inlet end of the third meter 54 of the series, and through another branch conduit 33 with the interior of the bell or float of the second gauge 58 of the series. As shown at 63 the rotatable shaft of said second gauge is relatively shorter than the aforementioned shaft 63, to provide clearance between the grooved wheel 65 attached to the former, and the aforementioned cable 63. A relatively shorter endless cable H extends between the last mentioned wheel 65 and a second spool 8'!--and said cable H has attached thereto at a suitable point an indicating and recording stylus 12 for cooperation with the intermediate section 70* of the record chart it. Stylus i2 cooperates with the chart section lil to continuously indicate and record the combined proportional or percentage value of the constituents removed in the two absorption chambers 25 and 25 If it is desired to know the proportional or percentage value of carbon monoxide removed in chamber 25 this may be readily calculated by merely subtracting the instantaneous value recorded upon chart section Ill from the corresponding value recorded upon chart section 10 The further reduced volumetric flow of test gas when discharged from the third meter 54 is passed through the third absorbing chamber 25 to effect removal of another constituent, such as oxygen. The outlet end of chamber 25 communicates through a branch conduit 21 with the inlet end of the fourth meter 55, and through another branch conduit 33 with the interior of the bell or float of the third, or right-hand, gauge of the series. The shaft 53 of the last mentioned gauge is sufficiently short to provide clearance between the wheel 65 attached thereto and the cable H. A relatively shorter endless cable 13 is interposed between the wheel attached to shaft 63' and a third spool 61*, said cable having attached thereto at a predetermined point an indicating and recording stylus 14 which cooperates with the right-hand section Til of chart 1D to continuously indicate and record the combined instantaneous proportional or percentage values of the three constituents (carbon dioxide, carbon monoxide and oxygen) removed from the test gas. If it is desired to know the instantaneous proportional or percentage value of the oxygen in the test gas it is only necessary to subtract the value shown on chart section 10 from the value shown simultaneously on chart section lii Although I have illustrated in Fig. 2 means for ascertaining and indicating and recording the proportional or percentage values with respect to three constituents of the test gas, it is to be understood that additional meters and gauges may be incorporated in the system, with a corresponding addition to the number of chart sections and parts to be associated therewithwhereby the proportional or percentage value of other constituents of the test gas may be ascertained and indicated and recorded.

I claim:

1. In a liquid pressure gauge of the type wherein the interior of a prover bell floating on a liquid is exposed to a fluid having a variable degree of pressure the value of which it is desired to ascertain, and wherein the level of the liquid within the bell varies in accordance with the pressure of said fluid and thereby also varies the volume of the fluid within said prover bell, means for maintaining said volume substantially constant regardless of the pressure of said fluid comprising, in combination, a displacement member partially immersed in said liquid and movable in a vertical direction to raise or lower the level of said liquid, spring tension means connected between said prover bell and said movable displacement member whereby upon an increase in the level of said liquid the tension of said spring means is decreased, and vice versa, and actuating means responsive to changes in the vertical posi tion of said bell and connected to said movable displacement member for selectively raising or lowering said last mentioned member whereby the liquid level .within said bell and consequently the volume of fluid within said bell are maintained substantially constant.

2. A gauge comprising, in combination, a container, a body of liquid partially filling said container, a prover bell floating upon said body of liquid, means for subjecting the exterior of said bell and the upper surface of said body of liquid to a predetermined substantially constant degree of pressure, means for subjecting the interior of said bell to a variable degree of pressure the value of which it is desired to ascertain, a displacement member partially immersed in said liquid and movable in opposite directions to increase or decrease the level of said body of liquid, actuating means responsive to changes in the vertical position of said bell and connected to said movable displacement member for selectively raising or lowering said liquid level in accordance with said changes in vertical position of said bell, a tension spring connected between said bell and said displacement member whereby upon an increase in the level of said body of liquid the tension of said spring is decreased, and vice versa, and means movable with and in a direction corresponding to the movement of said displacement member, said last mentioned means being adapted to continuously indicate the variable value of pressure within said bell.

3. A pressure gauge comprising, in combination, a container, a body of liquid partially filling said container, a prover bell floating upon said body of liquid and having its interior subject to a variable degree of pressure the value of which it is desired to ascertain, said body of liquid having its upper surface and said prover bell having its exterior surface exposed to atmospheric pressure, a displacement m mber partially immersed in said liquid and movable in opposite directions to raise or lower the level of said body of liquid, a tension spring connected between said movable displacement member and said bell whereby upon an increase in the level of said body of liquid the tension of said spring is decreased, and vice'versa, actuating meansresponsive-to changes in the vertical position of said bell and connected to said displacement member for-selectively moving said last mentioned member to raise orlower the level of said body of liquid in accordance with changes in said vertical position whereby the levelof the liquid within said'bell remains substantially constant with respect to said bell, and means movable with and in a direction corresponding to the movement of said displacement member, said last mentioned means being adapted to continuously indicate the variable va'lueof pressure within said bell.

4; Ina pressure gauge, in combination, a container, a' body of mercury partially filling. said container, a prover bell floating upon said body of mercury, means'for subjectingrthe exterior of said bell and the upper surface of said body of mercury to'atmospheric pressure, means for sub jecting the interior of said'bell to a variable degree of pressure the value of which it is desired to ascertain, a displacement member partially immersed in said mercury and movable in opposite" directions to increase or decrease the level of'said body of mercury, a tension spring connected-between said movable member and said bell'whereby upon an increase in the level of said body of mercury the tension of said spring is decreased; and vice versa, a reversible electric REFERENCES CITED The following. references are of record in the file of this patent:

UNITED STATES PATENTS umber Name Date 1,174;241 Earl Mar. '7, 1916 1,682,602 Dawley Aug. 28, 1928 1,700,852 Packard Feb. 5, 1929 1,877,810 Chamberlain Sept. 20, 1932 2,363,174 Green et a1. Nov. 21, 1944 FOREIGN PATENTS Number Country Date 564,871 Germany Nov. 24, 1932 

